The major goals of these studies are to elucidate the individual roles of COX-1 and COX-2 in normal physiology and in various pathological states. Specifically, effort within the laboratory has focused on using COX-1 and COX-2 deficient mouse ES cells and COX specific inhibitors to study the roles of COX-1 and COX-2 in endothelial cell development. Endothelial cell ifferentiation was measured immunohistochemically by the appearance of CD-31 staining cord like structures of cells and the appearance of VEGF receptors on Western analysis. Our studies indicated that neither the deficiency of COX-1 or COX-2 inhibited mouse ES cell differentiation into endothelial-like cells in vitro. However, studies with COX-1 and COX-2 selective inhibitors have indicated that the COX-2 inhibitors blocked endothelial-like cell development even in COX-2-/- ES cells, suggesting that a COX-2 independent mechanism was responsible.